Ion-modal inconsistently doesn't add z-index inline style

Sometimes but not always, my modal appears in the markup but is not displayed.

I can see the when the modal does work and displays it has an inline style added z-index: 9999

Sometimes this isn’t added and therefore doesn’t display.

Is there a fix for this?

I have added

ion-modal {
  z-index: 9999;
}

to app.core.scss which works for showing the modal but stops my ion-select inside the modal from being visible

Still using beta-10